1. Field of the Invention
The present invention relates to a laser working method, for example, a method for producing with such laser working method an ink jet recording head for discharging ink droplets and depositing such ink droplets on a recording medium, an ink jet recording head or a micromachine produced with such method, and a laser working method capable of fine working of complex material or complex shape such as an IC or a hybrid IC.
2. Related Background Art
For fine working of a structured article requiring a fine structure and high precision, there has been employed a laser working method employing an ultraviolet laser.
Such fine working can be exemplified by working of ink flow paths and ink discharge ports of an ink jet recording head.
The Japanese Patent Application Laid-Open No. 2-121842 and No. 2-121845 disclose high precision working of forming ink flow paths and ink discharge ports with an excimer laser which is a representative ultraviolet laser. The excimer laser is capable of emitting ultraviolet light of a short pulse (15 to 35 ns) by discharge excitation of mixed gas of rare gas and halogen gas, with an oscillation energy of several hundred mJ/pulse and a pulse repeating frequency of 10 to 500 Hz. When the surface of polymer surface is irradiated with a short-pulsed ultraviolet light of such high intensity, there is generated an ablative photodecomposition (APD) process in which the irradiated portion instantaneously decomposes and scatters with a plasma light emission and an impact sound, whereby so-called laser ablation working of polymer resin is made possible.
Among the conventional lasers employed for such working, the widely employed YAG laser can form a hole but generates a coarse edge face, while the CO2 laser emitting infrared light is associated with a drawback of generating a crater around the formed hole. Such laser working methods are laser thermal working in which the working is achieved by converting optical energy into thermal energy, so that the shape of the workpiece (the object to be worked) is often destructed and fine working is difficult to achieve. On the other hand, the laser ablation working utilizing the excimer laser, based on sublimation etching by a photochemical reaction breaking the covalent bond of carbon atoms, does not easily destruct the shape of the workpiece and can therefore achieve working of very high precision.
The laser ablation working method means a working method by sublimation, not through a liquid phase, by a laser.
Particularly in the field of ink jet technology, it is well known that the technology has undergone a remarkable progress to the present state by the adoption of the laser ablation working technology utilizing such excimer laser.
With the practical adoption of such laser working technology with excimer laser, there have been found the following phenomena.
The pulse oscillation time of the irradiating laser is about several ten nanoseconds in case of the excimere laser which is an ultraviolet laser or about 100 picoseconds to several nanoseconds in case of an ultraviolet laser of high frequency oscillation of the YAG laser, but all the laser beam falling on the workpiece is not consumed for cleaving the covalent bonds of the atoms.
Because of the presence of such optical energy not consumed in cleaving the covalent bonds of the atoms, the laser worked portion of the workpiece scatters before being completely decomposed, thereby forming by-products around the working area.
Also a part of the optical energy not consumed in cleaving the covalent bonds of the atoms is converted into thermal energy.
Also, as the energy density of the excimer laser remains at the level of 100 megawatts at maximum in the oscillation pulse, the subliming ablation working is not easily applicable to the materials of high thermal conductivity such as metals, ceramics or mineral substances (such as silicon) or materials of low light absorption such as quartz or glass but can principally employed for organic resins.
These phenomena are unavoidable in using the excimer laser, and various technologies have been proposed to avoid the influences of these phenomena on the actual ink jet head.
For example, a step of removing the by-products is conducted, since the ink discharge ports may be clogged if the ink jet recording head is assembled while such by-products still remain.
Also, as the conversion of a part of optical energy into thermal energy may cause thermal expansion or partial fusion of the workpiece in the course of working, there is employed a material of a high glass transition point or a reduced working pitch.
Besides, since these technologies do not fundamentally resolve these phenomena, there are practically encountered various limitations in conducting the laser working.
On the other hand, a higher definition in the image quality is being requested for the ink jet recording head, and the density of arrangement of the ink discharge ports or the ink flow paths, conventionally in a range of 300 to 400 dpi, is now requested to be elevated to 600 dpi or even 1200 dpi.
Therefore, there is requested a method capable of forming the discharge ports and the ink flow paths with a small pitch or a small dimension, such as an arrangement pitch of 50 xcexcm or less and a working diameter of 20 xcexcm or less, with a high precision. However the above-mentioned phenomena associated with the exciver laser become more conspicuous as the working pitch or the working diameter becomes smaller, and are posing limitations in producing the ink jet head of high precision as mentioned above.
In consideration of the foregoing, the present inventor, having recognized that the aforementioned phenomena are based on the laser ablation working utilizing the ultraviolet laser exemplified by the excimer laser, and have made intensive investigations not restricted in the field of the conventional technologies and have reached a novel laser ablation technology that is capable of fundamentally resolving these phenomena, also adapting to the fine working technologies ever advancing hereafter and also expanding the adaptability to various applications.
In consideration of the foregoing, an object of the present invention is to provide a laser working method free from generation of by-products and fundamentally avoiding accumulation of thermal energy, generated in the course of laser working, in the workpiece such as a resin, thereby achieving highly precise working without fusion or thermal expansion of the workpiece, a method for producing an ink jet recording head utilizing such laser working method, and an ink jet recording head produced by such producing method.
Another object of the present invention is to provide a laser working method capable of forming a fine structure in a workpiece composed of plural materials by a simple working step, a method for producing an ink jet recording head utilizing such laser working method, and an ink jet recording head produced by such producing method.
Still another object of the present invention is to provide a laser working method capable of simplifying an alignment step, improving the precision such as the positional precision of an internally structured member and reducing the manufacturing cost, a method for producing an ink jet recording head utilizing such laser working method, and an ink jet recording head produced by such producing method.
Still another object of the present invention is to provide a laser working method capable of improving the working efficiency by constructing the workpiece so as to absorb the radiation energy of laser, a method for producing an ink jet recording head utilizing such laser working method, and an ink jet recording head produced by such producing method.
Still another object of the present invention is to provide a laser working method capable of preventing speckle interference and reducing the damage by the laser beam on the mask, thereby enabling the working of a workpiece by projection of a large-area pattern, a method for producing an ink jet recording head utilizing such laser working method, and an ink jet recording head produced by such producing method.
Still another object of the present invention is to provide a method for producing an ink jet recording head, capable of suppressing speckle interference and effecting laser working from the outer side of an ink discharge port forming plate (from the ink discharge side) to form a tapered shape that is symmetrical with respect to the axis of ink discharging direction and gradually thinning toward the end and capable of easily forming a tapered shape, tapering toward the end, with a uniform and large tapering angle or with a uniform and variable tapering angle, an ink jet recording head produced by such producing method and a laser working method.
The above-mentioned objects can be attained, according to the present invention, by a laser working method, a method for producing an ink jet recording head utilizing such laser working method, and an ink jet recording head produced by such producing method, featured as described in the following items (1) to (37):
(1) A laser working method for conducting laser ablation working on a workpiece by irradiating the workpiece with laser beam, comprising the steps of:
in working by projecting a mask pattern with laser beam, employing laser beam of plural pulses having a very high energy density in space and time, emitted from a laser oscillator that can oscillate with a pulse radiation time of 1 picosecond or less; and
conducting scanning illumination by a relative movement of a source of the laser beam and the mask pattern.
(2) The laser working method according to item (1), wherein the relative movement between the source of the laser beam and the mask pattern is conducted by a reciprocating movement in a direction perpendicular to the optical axis of the laser beam, asynchronously with the laser oscillation, and the form of the mask pattern is formed stepwise and in succession on the workpiece.
(3) The laser working method according to item (2), wherein the relative movement between the source of the laser beam and the mask pattern is conducted by moving the mask relative to the laser beam.
(4) The laser working method according to item (3), wherein the mask comprises a rolled film bearing a predetermined pattern, and the movement of the mask pattern is achieved by feeding the rolled film by winding means and rewinding means into the optical path of the laser beam.
(5) The laser working method according to item (3) or (4), wherein the ablation working of the workpiece is conducted by moving the workpiece in a direction perpendicular to the optical axis of the laser beam, in synchronization with the movement of a pattern image from a projection lens, resulting from the movement of the mask.
(6) The laser working method according to any of items (1) to (3), wherein the projection magnification of the projection lens which projects the mask is {fraction (1/20)} or less in the absolute value.
(7) The laser working method according to item (2), wherein the relative movement between the source of the laser beam and the mask pattern is conducted by scanning illumination of the mask pattern by the laser beam.
(8) The laser working method according to item (7), wherein the scanning illumination is conducted by illuminating light comprising laser beam from a laser oscillator condensed on the mask through a deflection scanning device and which is asynchronous with the laser oscillation.
(9) The laser working method according to item (8), wherein the laser working is conducted by scanning illumination through an optical system which converts the laser beam from the laser oscillator into a ring-shaped beam.
(10) The laser working method according to item (9), wherein the optical system for converting the laser beam from the laser oscillator into the ring-shaped beam comprises mutually opposed lenses of a conical shape and the distance of the mutually opposed conical lenses is rendered variable in the direction of optical axis, whereby the external shape of the ring-shaped beam can be expanded or contracted.
(11) The laser working method according to item (1), wherein the wavelength of the laser beam is within a range of 350 to 1000 nm.
(12) The laser working method according to item (1), wherein the pulse radiation time of the laser beam is 500 femtoseconds or less.
(13) The laser working method according to item (1), wherein the workpiece comprises a resin, Si or an Si compound.
(14) The laser working method according to item (1), wherein the laser oscillator is provided with a light propagation space compressing device.
(15) The laser working method according to item (14), wherein the light propagation space compressing device comprises chirping pulse generation means and vertical mode synchronization means utilizing the optical wavelength dispersion characteristics.
(16) The laser working method according to item (14), wherein the light propagation space compressing device is composed by a vertical mode synchronization method utilizing the optical wavelength dispersion characteristics of chirping pulse generation means and a diffraction phase grating.
(17) A method for producing an ink jet recording head comprising an ink discharge port for discharging ink droplets to be attached to a recording medium, a liquid chamber for holding ink to be supplied to the ink discharge port, an ink flow path communicating the liquid chamber with the ink discharge port, an energy generation element provided in a part of the ink flow path and serving to generate energy for ink discharge, an ink supply aperture for ink supply from the outside to the liquid chamber, in which a member constituting at least a part of the ink flow path is worked by laser working, wherein:
the laser working, conducted by projecting a mask pattern with the laser beam, employs laser beam of plural pulses having a very high energy density in space and time, emitted from a laser oscillator that can oscillate with a pulse radiation time of 1 picosecond or less; and scanning illumination is conducted by a relative movement of a source of the laser beam and the mask pattern.
(18) The method for producing an ink jet recording head according to item (17), wherein the relative movement between the source of the laser beam and the mask pattern is conducted by a reciprocating movement in a direction perpendicular to the optical axis of the laser beam, asynchronously with the laser oscillation, and the shape of the mask pattern is formed stepwise and in succession on the workpiece.
(19) The method for producing an ink jet recording head according to item (18), wherein the relative movement between the source of the laser beam and the mask pattern is conducted by moving the mask relative to the laser beam.
(20) The method for producing an ink jet recording head according to item (19), wherein the mask comprises a rolled film bearing a predetermined pattern, and the movement of the mask pattern is achieved by feeding the rolled film by winding means and rewinding means into the optical path of the laser beam.
(21) The method for producing an ink jet recording head according to item (19) or (20), wherein the ablation working of the workpiece is conducted by moving the workpiece in a direction perpendicular to the optical axis of the laser beam, in synchronization with the movement of a pattern image from a projection lens, resulting from the movement of the mask.
(22) The method for producing an ink jet recording head according to any of items (17) to (19), wherein the projection magnification of the projection lens which projects the mask is {fraction (1/20)} or less in the absolute value.
(23) The method for producing an ink jet recording head according to item (18), wherein the relative movement between the source of the laser beam and the mask pattern is conducted by scanning illumination of the mask pattern by the laser beam.
(24) The method for producing an ink jet recording head according to item (23), wherein the scanning illumination is conducted by illuminating light comprising laser beam from a laser oscillator condensed on the mask through a deflection scanning device and which is asynchronous with the laser oscillation.
(25) The method for producing an ink jet recording head according to item (24), wherein the laser working is conducted by scanning illumination through an optical system which converts the laser beam from the laser oscillator into a ring-shaped beam.
(26) The method for producing an ink jet recording head according to item (25), wherein the optical system for converting the laser beam from the laser oscillator into the ring-shaped beam comprises mutually opposed lenses of a conical shape and the distance of the mutually opposed conical lenses is rendered variable in the direction of optical axis, whereby the external shape of the ring-shaped beam can be expanded or contracted.
(27) The method for producing an ink jet recording head according to item (17), wherein the member constituting a part of the ink flow path comprises a recessed portion or a penetrating hole, and the recessed portion or the penetrating hole is simultaneously formed in plural units with a predetermined distance by laser beam irradiation through a mask having a pattern of plural apertures formed at a predetermined pitch.
(28) The method for producing an ink jet recording head according to item (27), wherein the recessed portion is a groove to constitute the ink flow path.
(29) The method for producing an ink jet recording head according to item (27), wherein the penetrating hole is to constitute the ink discharge port.
(30) The method for producing an ink jet recording head according to item (17), wherein the wavelength of the laser beam is within a range of 350 to 1000 nm.
(31) The method for producing an ink jet recording head according to item (17), wherein the pulse radiation time of the laser beam is 500 femtoseconds or less.
(32) The method for producing an ink jet recording head according to item (17), wherein a member constituting at least a part of the ink passage including the ink discharge port, ink flow path, liquid chamber and ink supply aperture comprises a resin.
(33) The method for producing an ink jet recording head according to item (17), wherein a member constituting at least a part of the ink passage including the ink discharge port, ink flow path, liquid chamber and ink supply aperture comprises Si or an Si compound.
(34) The method for producing an ink jet recording head according to item (17), wherein the laser oscillator is provided with a light propagation space compressing device.
(35) The method for producing an ink jet recording head according to item (34), wherein the light propagation space compressing device comprises chirping pulse generation means and vertical mode synchronization means utilizing the optical wavelength dispersion characteristics.
(36) The method for producing an ink jet recording head according to item (34), wherein the light propagation space compressing device is composed by a vertical mode synchronization method utilizing the optical wavelength dispersion characteristics of chirping pulse generation means and a diffraction phase grating.
(37) An ink jet head produced by the method for producing an ink jet recording head according to item
(17).